1. Field of the Invention
This invention relates to an anti-bacterial, antifungal silicone rubber composition which imparts antibacterial and antifungal properties to silicone rubber products for improving the living environment, prolonging the lifetime and improving food hygienics.
2. Prior Art
In the recent years, silicone rubber is used in a wide variety of applications covering electronic, automotive, building, medical and food industries because of its excellent properties including weatherability, electrical properties, low compression set, heat resistance, and low-temperature resistance. Typical uses include packings or gaskets in refrigerators, electric rice cookers, and electric pots as exemplary home appliances, packings in food-keeping containers, and medical tubes like catheters. The demand for silicone rubber is increasing and there is a need for developing a silicone rubber having more improved properties.
It was recently proposed to add antifungal agents to render silicone rubber antifungal. Most antifungal agents used heretofore are organic agents such as benzimidazole, and methylsulfonyl. Since these organic agents are susceptible to a temperature change, light like ultraviolet radiation, a humidity change, or trace components in the environment and can be deteriorated thereby, their effect does not last long.
Attempts have been made for sustaining the antifungal effect by coating or capsulating such organic antifungal agents or by adding active substances to the silicone polymer. These attempts, however, suffer from several problems, for example, (1) an increased cost, (2) failure to exert effect because organic antifungal agents can be buried in silicone rubber, (3) difficultly of storage because products treated with antifungal agents gradually deteriorate in effect even if they are not in use, and (4) degradation by heat vulcanization because organic antifungal agents are degraded thereby to drastically drop their effect and discolor silicone rubber moldings.
More recently, inorganic antifungal and antibacterial agents were developed. For example, Japanese Patent Application Kokai (JP-A) No. 1226/1993 discloses water-soluble glass containing a silver ion, zinc ion, copper ion or a mixture thereof. JP-A 20559/1990 discloses blending of protein silver. JP-A 93360/1992 discloses blending of ZnO, MgO, propionates or a mixture thereof. These proposals, however, suffer from several problems. For example, it is difficult to carry sufficient ions. Some agents cause silicone rubber to be discolored. Some agents lose an ion carrying ability and hence, their effect by high-temperature treatment. Some agents must be added in large amounts in order to maintain antifungal activity. Some agents are prohibited from the standpoint of food hygienics.